The production and characterization of IgE will be studied in different species especially in rabbits, mice, rats and guinea pigs. In rabbits, characterization of other than IgE immunoglobulin classes (which mediate immediate anaphylactic reactions such as passive cutaneous anaphylaxis) will also be studied. The antibody classes will be characterized, especially with regard to their dependence on complement for provoking this type of anaphylactic reaction. In mice and rats the role of parasitic infections will be studied on antibody production, especially on IgE and the role, if any, of parasitic infections with nematodes such as Nippostrongylus brasiliensis on production and potentiation of antibodies for defined chemical haptens such as dinitrophenol. This would permit the study of the role of the helper cells and using specific antitheta sera produced in congeneic animals (for all histocompatibility antigens except for the theta antigen) the eventual role of theta antigenic determinant bearing cells (potentiation and or hindrance) will be determined. Rat basophilic leukemia will be used to further study immunoglobulin receptors on basophilic cells, described for the first time in our laboratory. Bibliographic references: Further studies on the inheritance of responsiveness to Pertussis HSF in mice. Int. Archs Allergy appl. Immuno. 48, 11, 1975. Ovary, Z. & Caiazza, S., PCA reactions with mouse antibodies in mice and rats. Zoltan Ovary, Steven S. Caiazza and Somei Kojima, Inter. Arch, Allergy appl. Immun. 48, 16, 1975.